Question

cos 4 a/cos 2 a -sin 2a​

Answer 1

$\displaystyle\bf\\\frac{Cos4\alpha }{Cos2\alpha -Sin2\alpha } =\frac{Cos^{2} 2\alpha -Sin^{2} 2\alpha }{Cos2\alpha -Sin2\alpha } =\\\\\\=\frac{(Cos2\alpha -Sin 2\alpha )\cdot(Cos2\alpha +Sin2\alpha)}{Cos2\alpha -Sin2\alpha } =Cos2\alpha +Sin2\alpha$